Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. The fuel vapors may be stored in a fuel vapor canister coupled to the fuel tank which contains adsorbent material, such as activated carbon, capable of adsorbing hydrocarbon fuel vapor.
The fuel tank may be further coupled to a vapor recovery line (vapor recirculation line) which may also be coupled to the fuel vapor canister and the fuel filler neck. The vapor recovery line may be configured to circulate and/or hold a percentage of refueling vapors, thus limiting the rate of fuel vapor canister loading. Further, depending on the fuel dispenser, the fuel vapors within the vapor recovery line may be returned to the fuel dispenser, thus limiting the total fuel vapor stored within the fuel vapor canister for a given refueling event.
However, if the vapor recovery line becomes blocked, fuel vapor will not circulate through the vapor recovery line, and the canister loading rate (and total load) will increase. Unlike other blockages in the emissions control system, a blockage in the vapor recovery line may not necessarily result in pre-mature shutoff of the fuel dispenser, and may thus go undiagnosed. This may lead to an underestimation of canister load following refueling, which may in turn lead to an increase in bleed emissions if canister purge operations are not updated to accurately reflect the current canister load. While the fuel tank pressure during the refueling event can also be used to estimate the canister loading rate, the fuel tank pressure may not increase in accordance with a vapor recovery line blockage, and may thus not provide an accurate reflection of canister loading in the case of degradation.
The inventors herein have recognized the above issues, and have developed systems and methods to at least partially address them. In one example, a method is provided, comprising indicating a fuel vapor canister load based on a steady-state pressure in a vapor recovery line during a refueling event; and adjusting a canister purging operation in response to the indicated fuel vapor canister load. Restrictions in the vapor recovery line may increase the rate of fuel vapor canister loading during a refueling event. In this way, an accurate canister load may be determined following a refueling event, and canister purging operations adjusted accordingly.
In another example, a fuel system for a vehicle is provided, comprising a fuel tank coupled to a fuel vapor canister, a fuel filler neck coupled to the fuel tank, a vapor recovery line coupled between the fuel tank and the fuel filler neck, a vapor recovery line pressure sensor coupled within the vapor recovery line, and a controller with instructions stored in non-transitory memory, that when executed cause the controller to monitor pressure in the vapor recovery line during a refueling event, and indicate a fuel vapor canister load based on a steady-state vapor recovery line pressure during the refueling event. The vapor recovery line pressure may be compared to an expected vapor recovery line pressure assuming an intact vapor recovery line. In this way, a percent restriction in the vapor recovery line may be diagnosed and downstream operations adjusted accordingly.
In yet another example, method for a fuel system is provided, comprising responsive to a refueling request, opening a fuel tank isolation valve coupled between a fuel tank and a fuel vapor canister, indicating a pre-refueling canister load based on a canister load and a fuel tank pressure prior to opening the fuel tank isolation valve, monitoring a fuel level over time and a pressure in a vapor recovery line over time during a refueling event, indicating a rate of fuel vapor canister loading based on a steady-state fuel level rate of change and further based on a steady-state vapor recovery line pressure during the refueling event, indicating an updated canister load based on the pre-refueling canister load and the rate of fuel vapor canister loading during the refueling event, and updating a canister purge schedule based on the updated canister load. In this way, bleed emissions may be reduced, as the canister loading status may otherwise be underestimated based on an expected canister loading rate that does not take vapor recovery line degradation into account.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.